Camshaft adjusters are used to change the timing for the opening or closing of the valves. The fixed angular relationship between the camshaft and the crankshaft which drives it is nullified as a result, and the timing can be optimally adjusted in dependence upon the speed and other parameters. Camshaft adjusters enable a relative rotation of the camshaft to the crankshaft.
Known vane-cell camshaft adjusters have a rotor with a plurality of radially projecting vanes which by the force of a spring are pressed radially outwards against a stator casing. A plurality of stops, which project radially inwards, are formed on the stator, which limit the adjusting movement of the rotor in both directions of rotation if the vanes run against the stops. The leading edges of the vanes lie on the stator so that between one vane side and the adjacent side of a stop of the stator, a chamber is formed in each case, into which a fluid, as a rule, the engine oil, is supplied through a valve which is allocated to the camshaft adjuster. The stator on one hand serves for separating and sealing of the fluid chambers and on the other hand for the fixing of the timing adjustment angle between the camshaft and the crankshaft.
The rotor of the camshaft adjuster during assembly is connected by a screw to the camshaft with frictional locking. For creation of the frictional locking, the rotor (rotary piston) of the adjuster, by the pretensioning force of the central screw, is pressed by its lateral flange face onto the corresponding side face of the camshaft. The frictional locking has to transmit from the drive the driving torque and possible axial or radial forces. As a result, a relatively high pretensioning force has to be introduced. However, it has been proved that in the rotor, on the side facing the camshaft, relatively high tensile stresses are created in the slot base of the vane slots. In addition, due to the transmission of the camshaft driving torque from the drive to the output of the adjuster, high tensile stresses are introduced in the vane slot as a result of the supporting of the vane in the vane slot. As a result, there takes place a superimposition of the forces and stresses and, as a consequence, a high stress of the material.
The use of materials with a higher strength, however, should be avoided, since materials of higher strength in most cases require expensive and costly manufacturing technologies. Also, the increasing of the width and/or the diameter of the rotor is no practical solution, since these measures lead to an increased weight and to increased inertia. The mere increasing of the radius in the slot base over the width of the rotor is not possible, since the secure guiding of the vane is then possibly no longer ensured. Furthermore, there is the risk that the vane spring, which is installed on the slot base of the vane slot, changes its position.